A fluid driven turbine apparatus disclosed in Taiwanese Utility Model Patent No. M526625 is suitable for a hydroelectric power generation system. The fluid driven turbine apparatus includes an outer hollow member and a rotation unit disposed within the outer hollow member. The rotation unit includes a plurality of sideward flow passages extending radially and sideward from a center of the rotation unit. When water flows to the rotation unit and passes through the sideward flow passages to hit the outer hollow member, the rotation unit is driven to rotate for hydroelectric power generation. When large sand grains carried by the water pass through a gap formed between the rotation unit and the outer hollow member, they may abrade the rotation unit and the hollow member. To reduce abrasion caused to the fluid driven turbine apparatus, generally, introduction of large sand grains is avoided by disposing the fluid driven turbine apparatus in high water level region of a reservoir where the content of sands is low. However, water levels in some reservoirs are low and sand contents therein are high. Therefore, improvements over the existing fluid driven turbines are still necessary.